The present invention relates to an ink-jet printing apparatus and its printhead control method, and more particularly, to an ink-jet printing apparatus which performs printing on a recording medium by using an ink-jet printhead which performs printing by discharging ink, and having a temperature detection device which outputs a signal in correspondence with a temperature, and to acquisition of temperature information used for printhead control.
Printers which perform printing based on information of desired characters, images and the like on sheet-type print media such as print sheets and films are widely used as information output apparatuses of word processors, personal computers, facsimile machines.
Various printing methods for the printers are known, and in recent years, the ink-jet method especially attracts attention. In the ink-jet printing method, printing without contact with recording medium such as print sheet is possible, and color printing can be easily made, and further, printing with suppressed noise can be performed. The ink-jet printing is generally used as a serial printing method of performing printing by using a printhead which discharges ink in correspondence with desired print information while scan-moving the printhead in a direction orthogonal to conveyance direction of recording medium such as print sheet. This method is widely used since it enables a low-price and compact printing apparatus.
Conventionally, in the ink-jet printing apparatus, ink viscosity is influenced by temperature. To maintain a constant amount of ink to be discharged regardless of temperature, a temperature detection device is provided on a circuit board inside the apparatus main body or on a circuit board of the printhead. An environmental temperature (apparatus internal temperature) is obtained by various computations and correction processing on temperature information obtained by the temperature detection device. Then, energy to be applied to the ink-jet printhead is determined based on the obtained environmental temperature, by e.g. referring to a predetermined energy application table, and the ink-jet printhead is driven.
The temperature information as a basis for temperature control is obtained immediately before driving of the ink-jet printhead or when the printing apparatus is in a predetermined status. Further, generally, the results of various computations and corrections are temporarily stored in volatile storage means, and the obtained environmental temperature is not stored.
However, in the conventional arrangement where the temperature information is obtained at predetermined timing and the results of computations and corrections are temporarily stored in the storage means, if the temperature information is obtained in a state where the values of computations and corrections are lost, e.g., the power of the ink-jet printing apparatus is turned off then again turned on and printing is started, computations and corrections cannot be correctly performed. In such case, the obtained environmental temperature is different from an actual temperature.
In this case where the obtained environmental temperature is different from the actual temperature, the energy application table used for printhead driving is not appropriate to the actual temperature. Accordingly, ink discharge from the printhead is unstable, which degrades printing quality.
The present invention has its object to provide an ink-jet printing apparatus which obtains temperature information at appropriate timing in accordance with necessity, even if the power is interrupted during the operation, and produces a high-quality printed output by a stable printing operation.
According to the present invention, the foregoing object is attained by providing an ink-jet printing apparatus which performs printing on a recording medium by using an ink-jet printhead which performs printing by discharging ink, comprising: a temperature detection device that outputs a signal in correspondence with a temperature; temperature information acquisition means for obtaining temperature information based on the signal outputted from the temperature detection device; nonvolatile storage means for storing the temperature information obtained by the temperature information acquisition means; flag setting means for setting a flag indicating whether acquisition of the temperature information is necessary or not; and control means for checking a status of the flag after a power of the apparatus is turned on, and for controlling the acquisition of the temperature information in accordance with the status of the flag.
Another object of the present invention is to provide a printhead control method in the ink-jet printing apparatus for obtaining the temperature information at appropriate timing in accordance with necessity, even if the power is interrupted during the operation, and producing a high-quality printed output by a stable printing operation.
The foregoing object is attained by providing a printhead control method in an ink-jet printing apparatus which has a temperature detection device to output a signal in correspondence with a temperature and which performs printing on a recording medium by using an ink-jet printhead which performs printing by discharging ink, the method comprising: a temperature information acquisition step of obtaining temperature information based on the signal outputted from the temperature detection device; a storage step of storing the temperature information obtained at the temperature information acquisition step; a flag setting step of setting a flag indicating whether acquisition of the temperature information is necessary or not; and a control step of checking a status of the flag after a power of the apparatus is turned on, and controlling the acquisition of the temperature information in accordance with the status of the flag.
That is, in accordance with the present invention, in an ink-jet printing apparatus which has a temperature detection device to output a signal in correspondence with a temperature and which uses a printhead to perform printing by discharging ink, temperature information is obtained based on the signal outputted from the temperature detection device, then the obtained temperature information is stored into nonvolatile storage means, a flag indicating whether acquisition of the temperature information is necessary or not is set, a status of the flag is checked after a power of the apparatus is turned on, an the acquisition of the temperature information is controlled in accordance with the status of the flag.
In this arrangement, if a flag indicating whether acquisition of the temperature information is necessary is set e.g. based on the elapsed time since the beginning of status where the apparatus does not perform printing, the temperature information is obtained after a power of the apparatus is turned on, and the stored information is updated.
Accordingly, the temperature information can be obtained at appropriate timing in accordance with necessity, even if the power is interrupted during the operation, and a high-quality printed output can be produced by performing a stable printing operation.
Preferably, the temperature flag setting means sets a flag indicating that the acquisition of the temperature information is necessary, if elapsed time since the beginning of a status where the printing apparatus does not perform printing becomes predetermined time.
More preferably, if the elapsed time since the beginning of a status where said printing apparatus does not perform printing becomes first time, the flag setting means sets a flag indicating that acquisition of the temperature information is necessary, and if the elapsed time since the beginning of the status where the printing apparatus does not perform printing becomes second time which is longer than the first time, the control means controls to obtain the temperature information.
If the printhead is capped, the flag setting means may determine that the printing apparatus is in the status where the apparatus does not perform printing.
Preferably, the temperature information acquisition means obtains an environmental temperature by predetermined computation based on the signal outputted from the temperature detection device.
In this case, the temperature information acquisition means uses a correction value for the signal outputted from the temperature detection device in the predetermined computation.
The correction value may be obtained from a profile of the signal outputted from the temperature detection device.
If the temperature information is not stored in the storage means, the control means may control to obtain the temperature information.
The temperature detection device may be provided in the printing apparatus main body or in the printhead.
The temperature detection device may be a thermistor.
Preferably, the printhead discharges ink by utilizing thermal energy, and includes thermal energy transducers for generating thermal energy to be applied to the ink.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.